The present invention relates to an antenna device that performs wireless communication with an electronic key.
Immobilizer systems are installed in automobiles to prevent automobile theft by prohibiting starting of the engine. Japanese Laid-Open Patent Publication No. 2007-303171 describes such an immobilizer system. The immobilizer system of the publication includes a transponder arranged in an ignition key, a coil antenna arranged in a key cylinder, and a computer installed in a vehicle (steering column).
When a driver inserts the ignition key into the key cylinder device, the transponder of the ignition key transmits an ID code. The coil antenna in the key cylinder then receives the ID code from the transponder and transmits the ID code to the computer. The computer compares the received ID code with its ID code and permits starting of the engine when the two ID codes are in conformance. In this state, operation of the ignition key starts the engine.
The immobilizer system of each automobile has a unique ID code, which differs from those of other automobiles. Thus, the correct key cylinder, which incorporates electronic components, must be installed in each automobile. To prevent erroneous installation, a label or the like can be attached to the key cylinder. However, erroneous installation may occur not only when installing the key cylinder in an automobile but also when installing electronic components in the key cylinder device. Nevertheless, the installation of the correct electronic components cannot be determined from the outer appearance of the key cylinder device. In this regard, there is still room for improvements.